The coastal dynamics of the Central Ganges–Brahmaputra–Meghna Delta Coast, Bangladesh: implications for coastal development and sustainability

Abstract

The study analyzes satellite imagery, beach morphology, grain size, river discharge and bathymetry, and tidal water level along the central Ganges-Brahmaputra-Meghna (GBM) delta coast and examines the processes of coastal development. Integrated remote sensing and geographic information system (GIS) techniques were used to monitor coastal dynamics in the GBM delta from 1978 to 2023. The analysis shows that the west and central coasts eroded about 0.03–2.40 km and lost 14.54 km² of land during the study period. In contrast, the east coast advanced 0.09–1.42 km and gained 2.80 km². Beach slopes varied with the west coast having slope between 1° and 2°, and consisting of bimodal, poorly sorted, very fine-grained sand. The central and eastern coastline have slopes between 1° and 4°, and 3° and 5°, respectively, with unimodal, well-sorted to moderately well-sorted fine-grained sand. Statistical analysis of tidal water levels shows an increasing trend (8–12 mm yr⁻¹), while river discharge decreased by 22.57–55.94% during the period November to May due to the upstream dams, and channels were silted. On the east coast, characterized by weak longshore currents, there is minimal transfer of sediment to the sea, and the coastline advanced. Conversely, the current gets stronger when it moves to the west, and the coastlines experience the erosion. The coastal development of the area was influenced by unequal sediment supply and accommodation created at the river mouth due to the sea level rise (SLR). In addition to the natural factors, anthropogenic activities have also influenced the coastal sustainability in the study area.